1. Technical Field
Aspects of the present invention relate to a feeder unit to feed sheets contained in a tray into a feeding path, a sheet feeding device having the feeder unit, and an image forming apparatus having the sheet feeding device. More specifically, a feeder unit having a main frame and a secondary frame, whilst the secondary frame is capable of being installed in a correct position of the main frame easily, is provided. Further, a sheet feeding device having the feeder unit and an image forming apparatus having the sheet feeding device are provided.
2. Related Art
Conventionally, a sheet feeding device to separate a sheet from a sheet stack contained in a tray and forward the separated sheet in a feeding path has been known. The sheet feeding device has a feed roller, which is in a position to be in contact with a topmost sheet in the sheet stack, so that the topmost sheet can be separated from the sheet stack by contact friction generated between the topmost sheet and the feed roller whilst the feed roller rotates. In Japanese Patent Provisional Publications No. 2002-60068 and No. 2005-247521, for example, a sheet feeding device having a frame with a swingable arm portion and a feed roller to rotate at the swingable end of the arm portion is disclosed. Rotation force (torque) from a motor is conveyed to the fed roller through gears which are rotatably supported by the frame.
The frame to rotatably support the gears can be molded out of rather inexpensive materials (e.g., resin) in consideration of manufacturing cost and convenience, weight saving, etc. However, the frame is often subject to distortional stress, which can be caused by feeding load in the feed roller and driving torques of the motor. Therefore, it is required that the frame is made of a material with rigidity. Further, the frame is required to be molded with dimensional accuracy in order to avoid irregular feeding and misalignment in a feeding path, and to feed the sheets smoothly and uniformly.
Furthermore, because the gears are rotatable in the frame, bearings to hold the gears are subject to wear away due to rotating friction. When the bearings are abraded and eroded, positions to hold the gears may be displaced, and the rotating force of the motor may not be effectively conveyed to the feed roller. Therefore, the frame is required to be molded out of a material with abrasion resistance. Often, the material with high rigidity, easy moldability, and high abrasion resistance can be rather costly.
In order to overcome the above difficulties, it is possible to form the bearings and the frame separately in different materials and to attach the bearings to the frame afterwards. In this configuration, the frame can be made of a material with higher rigidity and moldability but lower abrasion resistance whilst the bearings can be made of a material with higher abrasion resistance. Thus, the frame and the bearings can be made of different materials which are suitable to respective components; i.e., the frame can be made of a material which is inexpensive and suitable to the frame, and the bearings can be made of a material which is inexpensive and suitable to the bearings.